Abstract
Two types of intraspecific nucleolar dominance/suppression are described for barley,Hordeum vulgare L. When the nucleolus organizing regions (NORs) originally belonging to chromosomes 6 and 7 are combined by translocation in one chromosome, NOR 6 is dominant over NOR 7. Neither significant loss of rDNA nor its hypermethylation is the reason for the reduced nucleolus forming activity of NOR 7. Intrachromosomal NOR suppression probably does not occur in isochromosome 6s, which has two NORs 6 in one chromosome. Meiotic and somatic pairing of the homologous arms might be the reason for early fusion of their nucleoli and thus for the lower than expected maximum number of interphase nucleoli. Variable suppression of a partial NOR (63) is described for descendants of crosses between translocation lines with split NORs 6 and 7. In these cases also, the reduced activity of the partial NOR 63 is not due to deletion of rDNA as shown by in situ hybridization. Unstable methylation of NOR 63 in heterozygous F1 individuals is probably the cause of this phenomenon.
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Schubert, I., Künzel, G. Position-dependent NOR activity in barley. Chromosoma 99, 352–359 (1990). https://doi.org/10.1007/BF01731723
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DOI: https://doi.org/10.1007/BF01731723